Ion source

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An ion source is an electro-magnetic device that is used to create charged particles. These are used primarily within mass spectrometers or particle accelerators.

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[edit] Mass spectrometry

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In mass spectrometry, an ion source is a piece of equipment used to ionize analyte molecules and, if necessary, free them from the solid or liquid phase. Once the analyte ions are free to move electric fields will direct them into the mass analyzer.

There are several types of ion sources:

[edit] Sonic spray ioniation

Main article: sonic spray ionization

Sonic spray ionization (SSI) is method for creating ions from a liquid solution, for example, a mixture of methanol and water.[1] A pneumatic nebulizer is used to turn the solution into a supersonic spray of small droplets. Ions are formed when the solvent evaporates and the statistically unbalanced charge distribution on the droplets leads to a net charge and complete desolvation results in the formation of ions.

[edit] In particle accelerators

In particle accelerators an ion source creates a particle beam at the beginning of the machine, the Source. The technology to create ion sources for particle accelerators depends strongly on the type of particle that needs to be generated: electrons, protons, H- ion or a heavy ion.

Electrons are generated with an electron gun, and there are many varieties of these.

Protons are generated with a plasma-based device, like a duoplasmatron or a magnetron.

H- ions are generated with a magnetron or a Penning source. A magnetron consists of a central cylindrical cathode surrounded by an anode. The discharge voltage is typically greater than 150 V and the current drain is around 40 A. A magnetic field of about 0.2 tesla is parallel to the cathode axis. Hydrogen gas is introduced by a pulsed gas valve. Caesium is often used to lower the work function of the cathode, enhancing the amount of ions that are produced.

For a Penning source, a strong magnetic field parallel to the electric field of the sheath guides electrons and ions on cyclotron spirals from cathode to cathode. Fast H-minus ions are generated at the cathodes as in the magnetron. They are slowed down due to the charge exchange reaction as they migrate to the plasma aperture. This makes for a beam of ions that is colder than the ions obtained from a magnetron.

Heavy ions are generated with an electron cyclotron resonance ion source. The use of electron cyclotron resonance (ECR) ion sources for the production of intense beams of highly charged ions has immensely grown over the last decade. ECR ion sources are used as injectors into linear accelerators, Van-de-Graaff generators or cyclotrons in nuclear and elementary particle physics. In atomic and surface physics ECR ion sources deliver intense beams of highly charged ions for collision experiments or for the investigation of surfaces. For the highest charge states, however, Electron beam ion sources (EBIS) are needed. They can generate even bare ions of mid-heavy elements. The Electron beam ion trap (EBIT), based on the same principle, can produce up to bare uranium ions and can be used as an ion source as well.

[edit] Theory of Operation

Gas flows through the ion source between the anode and the cathode. A positive voltage is applied to the anode. This voltage, combined with the high magnetic field between the tips of the internal and external cathodes allow a plasma to start. Ions from the plasma are repelled by the anode electric field. This creates an ion beam.[2]

[edit] Ion Source Applications

[edit] References

  1. ^ Hirabayashi A, Sakairi M, Koizumi H (1995). "Sonic spray mass spectrometry". Anal. Chem. 67 (17): 2878-82. doi:10.1021/ac00113a023. PMID 8779414. 
  2. ^ Ion Beam Sources. Advanced Energy. Retrieved on 2006-12-14.
  3. ^ Ion Beam Source Technology. Advanced Energy. Retrieved on 2006-12-14.

[edit] See also

[edit] External links

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Mass spectrometry
Mass • Mass spectrum • MS software
Ion source
EI  • CI  • IA  • FAB  • FD  • MALDI  • APCI  • ESI  • DESI  • GD  • ICP  • MIP  • TS  • DART
Mass analyzer
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MS/MS  • GC/MS  • LC/MS